Microwave ablation system

ABSTRACT

A microwave ablation catheter assembly is provided. A coaxial cable configured to connect to a microwave energy source at its proximal end and at its distal end to a distal radiating section. The coaxial cable includes inner and outer conductors and a dielectric positioned therebetween. An extended working channel is configured to receive the coaxial cable for positioning the coaxial cable adjacent target tissue. At least a portion of an inner surface of the extended working channel is electrically conductive. The electrically conductive inner surface of the extended working channel may function as a balun to maintain a balanced signal between the inner and outer conductors of the coaxial cable when the distal radiating section of the coaxial cable is energized.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of and priority to U.S.Provisional Application Ser. No. 62/041,773, filed on Aug. 26, 2014, theentire contents of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a microwave ablation catheterassembly. More particularly, the present disclosure relates to amicrowave ablation catheter assembly including an extended workingchannel having an electrically conductive inner surface that functionsas an electromagnetic shield or a balun for a microwave ablationcatheter of the microwave ablation catheter assembly.

2. Description of Related Art

Microwave ablation involves the application of high-frequencyelectromagnetic waves for treating various maladies including tumors inof organs like the liver, brain, heart, lung and kidney. It is knownthat tumor cells denature at elevated temperatures that are slightlylower than temperatures injurious to surrounding healthy cells.Therefore, known treatment methods, such as hyperthermia therapy, heattumor cells to temperatures above 41° C., while maintaining adjacenthealthy cells at lower temperatures to avoid irreversible cell damage.Such methods may involve applying electromagnetic radiation, ormicrowave energy, to heat tissue and include ablation and coagulation oftissue. In particular, microwave energy is used to ablate tissue todenature or kill the cancerous cells.

Conventional microwave ablation systems typically include one or moremicrowave ablation catheters coupled to a microwave energy source via afeedline, typically in the form of a coaxial cable. The microwaveablation catheters are placed adjacent target tissue and microwaveenergy is applied to the microwave ablation catheters causing localizedheating of target tissue. The microwave ablation catheter is typicallyrelatively thin and flexible to allow a user to navigate the microwaveablation catheter through a luminal network of one of the aforementionedorgans, e.g., a lung.

When treating malignancies of the lung, microwave ablation systems areoften used in conjunction with an electromagnetic navigation (EMN)system. One such system is described in U.S. Pat. No. 6,188,355 andpublished PCT Application Nos. WO 00/10456 and WO 01/67035, the entirecontents of which are hereby incorporated by reference. An EMN systemtypically includes a bronchoscope, a catheter assembly containing alocation sensor at its steerable distal tip, an extended working channelthat extends beyond the reach of the bronchoscope and becomes a pathwayto the target site for subsequent diagnostic tools, and a computersystem which provides the physician, or user, with navigational views ofthe lung. Once the bronchoscope is inserted into a patient's lungs, thecatheter assembly with the extended working channel is inserted into thebronchoscope. Using the navigation system and the steerable distal tip,the catheter assembly and extended working channel is navigated to atarget location. The catheter assembly is then removed, leaving theextended working channel in place. The microwave ablation catheter canthen be inserted into the extended working channel and directed to thetarget location.

As previously mentioned, the microwave ablation catheter is coupled tothe microwave energy source via a feedline, often in the form of anunbalanced coaxial cable. As a result of the coaxial cable beingunbalanced, there is often a loss of microwave energy along the coaxialcable. Additionally, substantial heating of the coaxial cable can occurduring delivery of microwave energy. In order to help minimize the lossof energy as a result of an unbalanced coaxial cable, microwave ablationcatheters that utilize a feedline in the form of a coaxial cable mayinclude a balun or choke. The balun or choke helps to balance thecoaxial cable of the microwave ablation catheter when microwave energyis transmitted to the radiating section of the microwave ablationcatheter to ablate tissue and substantially impede the current flowingdown the outer conductor which might lead to undesired heating of tissuealong the length of the ablation catheter.

While the aforementioned microwave ablation catheters are suitable fortheir intended purposes, the balun on the microwave ablation catheter isadded structure that increases the size of the microwave ablationcatheter, which, in turn, may decrease the flexibility of the microwaveablation catheter.

SUMMARY

As can be appreciated, an extended working channel having anelectrically conductive inner surface that functions as anelectromagnetic shield and/or a balun for a microwave ablation catheterof a microwave ablation system may prove useful in the surgical arena.

Aspects of the present disclosure are described in detail with referenceto the drawing figures wherein like reference numerals identify similaror identical elements. As used herein, the term “distal” refers to theportion that is being described which is further from a user, while theterm “proximal” refers to the portion that is being described which iscloser to a user.

As defined herein braided means made by intertwining three or morestrands, and while described as a braid, the actual construction is notso limited and may include other formations as would be understood bythose of ordinary skill in the art.

An aspect of the present disclosure provides a microwave ablationcatheter assembly comprising an ablation catheter and an extendedworking channel. The ablation catheter includes a coaxial cable having aproximal portion and a distal portion and a radiator disposed at thedistal portion of the coaxial cable. The coaxial cable further includesan inner conductor and an outer conductor. The proximal portion of thecoaxial cable is capable of being operatively connected to a microwaveenergy source. The extended working channel is configured to receive theablation catheter for positioning the radiator adjacent target tissue.The extended working channel includes an electrically conductive innersurface, wherein, upon application of microwave energy to the microwaveablation catheter assembly, energy conducted along the outer conductorof the coaxial cable is captured within the conductive inner surface ofthe extended working channel and prevented from affecting tissueadjacent the extended working channel.

The microwave ablation catheter assembly, including the ablationcatheter and extended working channel, may me placed within a patientusing a location sensing system. The extended working channel may alsoinclude a slot at its proximal end configured to releasably engage witha corresponding mechanical interface positioned on the ablationcatheter. The mechanical interface may also be configured to be moveablewith the slot to lock the distal radiating section of the coaxial cableinto at least one of a plurality of positions defined within the slot.Indicia may also be provided along the slot and may be configured torepresent quarter-wavelength increments. The extended working channelmay further comprise an insulator separating the electrically conductiveinner surface from tissue adjacent the extended working channel.

The ablation catheter of the microwave ablation catheter assembly mayfurther include one or more cooling catheters surrounding the coaxialcable and radiator to provide a pathway for a cooling medium, such as agas or liquid. The extended working channel may also provide for an openor closed pathway for a cooling medium to either circulate within orpass through the extended working channel.

An aspect of the instant disclosure provides a method ofelectrosurgically treating target tissue. An extended working channel,having at least a portion of an electrically conductive inner surface,is positioned adjacent target tissue. Thereafter, an ablation catheter,having an outer conductor, is inserted through the extended workingchannel such that a radiator of the ablation catheter extends beyond thedistal end of the extended working channel. Energy is then applied tothe ablation catheter such that the electrosurgical energy radiates fromthe radiator to electrosurgically treat the target tissue. Uponapplication of energy to the ablation catheter, any energy conductedalong an outer conductor of the ablation catheter is captured within theelectrically conductive inner surface of the extended working channel,preventing the energy from affecting tissue adjacent the extendedworking channel.

The method of electrosurgically treating target tissue may furtherinclude engaging a mechanical interface of the ablation catheter with atleast one mechanical interface defined along a slot provided on theextended working channel to lock the radiator of the ablation catheterin a position that is distal of the distal end of the extended workingchannel. The slot may be provided at a proximal end of the extendedworking channel and may be configured to releasably couple to amechanical interface positioned on the ablation catheter. Indicia mayfurther be provided along the slot which may representquarter-wavelength increments. The method may further include moving themechanical interface of the ablation catheter distally to lock theablation catheter into at least one other position within the slot toadjust a signal balance between inner and outer conductors of theablation catheter. The electrically conductive inner surface of theextended working channel may further include a braided configuration.

An aspect of the present disclosure provides a microwave ablationsystem. The microwave ablation system comprises a microwave energysource, an ablation catheter, and an extended working channel. Theablation catheter includes a coaxial cable, having a proximal portionand a distal portion, and a radiator disposed at the distal portion ofthe coaxial cable. The coaxial cable includes an inner conductor and anouter conductor, and the proximal portion of the coaxial cable isoperatively connected to the microwave energy source. The extendedworking channel is configured to receive the ablation catheter forpositioning the radiator adjacent target tissue. The extended workingchannel includes an electrically conductive inner surface, wherein, uponapplication of microwave energy to the ablation catheter, energyconducted along the outer conductor of the coaxial cable is capturedwithin the conductive inner surface of the extended working channel andprevented from affecting tissue adjacent the extended working channel

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein withreferences to the drawings, wherein:

FIG. 1 is a schematic illustration of an EMN system configured for usewith a microwave ablation catheter in accordance with an illustrativeembodiment of the present disclosure;

FIG. 2 is a perspective view of a microwave ablation catheter inaccordance with an embodiment of the instant disclosure;

FIG. 3A is a perspective view of the distal and proximal portions of anextended working channel of a catheter guide assembly shown in FIG. 1;

FIG. 3B is a transverse, cross-sectional view of one embodiment of theextended working channel shown in FIG. 3A; and

FIG. 4 is a perspective view of the microwave ablation catheterpositioned within the extended working channel and with a distalradiating section positioned within target tissue.

FIG. 5 is a perspective view of the microwave ablation catheterpositioned within a a metal hypo tube in accordance with the presentdisclosure.

DETAILED DESCRIPTION

The present disclosure is directed to a microwave ablation catheterassembly and a method for placement of a microwave ablation antennawithin a luminal structure such as the pathways of the bronchi in thelungs. Embodiments of the present disclosure include an un-chokedmicrowave ablation catheter, or microwave ablation catheter without abalun. Further embodiments are directed to a microwave ablation catheterwith a modified balun or choke. Still further embodiments of the presentdisclosure are directed to an improved microwave ablation catheterassembly having increased flexibility and a reduced number of componentswhile providing adequate therapeutic results.

Detailed embodiments of the present disclosure are disclosed herein;however, the disclosed embodiments are merely examples of thedisclosure, which may be embodied in various forms. Therefore, specificstructural and functional details disclosed herein are not to beinterpreted as limiting, but merely as a basis for the claims and as arepresentative basis for teaching one skilled in the art to variouslyemploy the present disclosure in virtually any appropriately detailedstructure.

FIG. 1 is an illustration of an EMN system 10 in accordance with thepresent disclosure. One such EMN system 10 is the ELECTROMAGNETICNAVIGATION BRONCHOSCOPY® system currently sold by Covidien LP. Typicallythe EMN system 10 includes a bronchoscope 72, one or more of twodifferent types of catheter guide assemblies 11 and 12, monitoringequipment 74, an electromagnetic field generator 76, a tracking module80, and a computer system 82. FIG. 1 shows a patient “P” lying on anoperating table 70 including an electromagnetic field generator 76.Placed on the patient “P” are a number of sensors 78, whose position inthe magnetic field generated by the electromagnetic field generator 76can be determined by the tracking module 80.

Each of the catheter guide assemblies 11, 12 includes an extendedworking channel 18 that is configured to receive a locatable guidecatheter 20 which includes a sensor 22. The locatable guide catheter 20is electrically connected to the EMN system 10, and particularly, thetracking module 80 enables navigation and tracking of the sensor 22within a luminal network, such as the lungs of a the patient “P”, toarrive at a designated target. As will be described in greater detailbelow, the extended working channel 18 is configured to receiveinstruments including the locatable guide catheter 20 and sensor 22,biopsy tools and microwave ablation catheter 16, as well as otherswithout departing from the scope of the present disclosure.

FIGS. 1 and 2 depict an ablation catheter 16 in accordance with oneembodiment of the present disclosure. The ablation catheter 16 includesa coaxial cable 38. Coaxial cable 38 includes a proximal end 41 thatcouples to a microwave energy source 90 (FIG. 1). A cooling source 92connects to the ablation catheter 16 to circulate cooling fluid as willbe described in greater detail below. As shown in greater detail in FIG.2, a distal radiating section 42 is provided at a distal end 44 of thecoaxial cable 38 and is configured to receive the inner conductor 40.The distal radiating section 42 may be formed from any suitablematerial. For example, in embodiments, the distal radiating section 42may be formed from ceramic or metal, e.g., copper, gold, silver, etc.The distal radiating section 42 may include any suitable configurationincluding but not limited to a blunt configuration, flat configuration,hemispherical configuration, pointed configuration, bar-bellconfiguration, tissue piercing configuration, etc. The distal radiatingsection 42 may couple to the distal end 44 of the coaxial cable viasoldering, ultrasonic welding, adhesive, or the like. In one embodimentthe distal radiating section 42 is sealed to the inner conductor 40 toprevent fluid from contacting the inner conductor 40.

Proximate the distal radiating section 42 is a feed gap 58, which isformed by removing a portion of the outer conductor 32 of the coaxialcable 38, to expose a dielectric 50. Proximate the feed gap 58 is theproximal radiating section 34, which is essentially just a portion ofthe outer conductor 32 of the coaxial cable 38. The proximal radiatingsection 34, the feedgap 58, and the distal radiating section 42 arelocated and dimensioned to achieve a specific radiation pattern for theablation catheter 16 and in combination are collectively known as theradiator 35 of the ablation catheter 16. As will be explained in greaterdetail below, the extension of the radiator 35 out of the extendedworking channel 18 enables the ablation of tissue, but the length ofthat extension can be varied as desired to adjust the shape and size ofthe ablation zone.

The outer conductor 32 is typically formed of a braided electricallyconducting material and extends along the dielectric 50, which ispositioned between the inner and outer conductors 40 and 32,respectively. One advantage of a braided configuration of the outerconductor 32 is that it provides the ablation catheter 16 with theflexibility to move within the relatively narrow luminal structures suchas the airways of the lungs of a patient. Additionally, through the useof flat wire braiding and follow on braid compression with anappropriately sized die, the cross sectional dimension of the braidedconductor may be minimized significantly in comparison to otherconductive structures, while maintaining an acceptable electricalperformance. The ablation catheter 16 may include one or more coolingcatheters 43 surrounding the coaxial cable 38 and radiator 35, thesecooling catheters 43 enable the passage of cooling medium over thecoaxial cable 38 and the radiator 35. The cooling catheters providepathways for cooling liquid or gas to reach the distal radiating sectionand remove heat generated by the application of energy. Cooling theradiator 35 and the coaxial cable 38 helps ensure that the ablationprocess is undertaken by the radiating waves of electromagnetic energyheating the tissue and not by localized heating of the coaxial cable 38or distal radiating section 42. Though shown in FIG. 2 with a singlecooling catheter 43, those of skill in the art will appreciate thatadditional co-luminal catheters may be employed to enable bi-directionalcooling medium flow with cooling medium passing the coaxial cable 38 anda first cooling catheter in a distal direction, reaching an areaproximate the distal end of the ablation catheter and then returning ina proximate direction between the first and a second cooling catheter.Further, as will be appreciated by those of skill in the art, thecooling catheters 43 are not entirely necessary and ablation catheter 16may be utilized in an uncooled or open cooled system as will bedescribed in greater detail below.

The flexibility of the ablation catheter 16 can be altered toaccommodate a specific surgical procedure, a specific luminal structure,specific target tissue, a clinician's preference, etc. For example, inan embodiment, it may prove advantageous to have an ablation catheter 16that is very flexible for movement through the relatively narrow airwayof the lungs of a patient. Alternatively, it may prove advantageous tohave an ablation catheter 16 include portions which are less flexible,e.g., where the ablation catheter 16 is needed to pierce or puncturetarget tissue.

One of the effects of ablation catheters is an energy loss that occursas energy intended for radiation into the tissue via the radiator 35 isreflected and/or travels proximally along the outer conductor 32 of thecoaxial cable 38, resulting in a less efficient system. In someinstances this energy can cause heating along the length of thecatheter, and affect the tissue proximate the outer conductor 32. Asnoted above, one methodology for preventing the traversal of this energyalong the outer conductor is to employ a balun or choke whicheffectively causes the energy to be reflected back towards the distalradiating section 42, and provide useful energy for the ablationprocess, rather than be an energy loss in the system. Methods of forminga balun for a flexible ablation catheter are described in U.S. patentapplication Ser. No. 13/834,581, filed on Mar. 15, 2013 by Brannan etal. entitled “Microwave Energy-Delivery Device and System,” the entirecontents of which are hereby incorporated by reference.

However, to improve the flexibility of the ablation catheter 16, oneembodiment of the present disclosure does not employ a balun or choke.Instead, the ablation catheter 16, as shown in FIG. 2, relies on theconstruction of the components of the catheter guide assemblies 11 and12, and particularly the extended working channel 18 to control theemission of microwave energy from the ablation catheter 16,substantially contain the energy traveling down the outer conductor 32,and prevent that energy from affecting tissue.

To further clarify how the construction of the catheter guide assemblies11, 12 affect the emission of microwave energy, reference is made toFIG. 1 which depicts two types of catheter guide assemblies 11, 12. Bothcatheter guide assemblies 11, 12 are usable with the EMN system 10 andshare a number of common components. Each catheter guide assembly 11, 12includes a handle 19, which is connected to an extended working channel18. The extended working channel 18 is sized for placement into theworking channel of a bronchoscope 72. In operation, a locatable guide20, including an electromagnetic sensor 22, is inserted into theextended working channel 18 and locked into position such that thesensor 22 extends a desired distance beyond the distal tip 25 of theextended working channel 18. The location of the sensor 22, and thus thedistal end of the extended working channel 18, within an electromagneticfield generated by the electromagnetic field generator 76 can be derivedby the tracking module 80, and the computer system 82. Catheter guideassemblies 11, 12 have different operating mechanisms, but each containa handle 19 that can be manipulated by rotation and compression to steerthe distal tip 25 of the extended working channel 18 and/or the sensor22 at the distal end of the locatable guide 20. Catheter guideassemblies 11 are currently marketed and sold by Covidien LP under thename SUPERDIMENSION® Procedure Kits. Similarly, catheter guideassemblies 12 are currently sold by Covidien LP under the name EDGE™Procedure Kits. Both kits include a handle 19, extended working channel18, and locatable guide 20. For a more detailed description of thecatheter guide assemblies including handle 19, extended working channel18, locatable guide 20, and sensor 22, reference is made tocommonly-owned U.S. patent application Ser. No. 13/836,203 filed on Mar.15, 2013 by Ladtkow et al, the entire contents of which are herebyincorporated by reference.

As shown in FIG. 3A, the extended working channel 18 includes aconductive inner layer 28 and an insulating layer 34. When an ablationcatheter 16 is inserted into the extended working channel 18, such thatthe radiator 35 extends beyond the distal end 25 of the extended workingchannel 18, and microwave energy is applied through the coaxial cable 38to the radiator, the conductive inner layer 28 forms an electromagneticbarrier preventing the radiation of the energy traveling down the outerconductor 32 from radiating to the tissue contacting the insulatinglayer 34. Essentially the conductive inner layer 28 creates a Faradaycage, significantly limiting the transmission of the energy through theextended working channel 18. The insulating layer 34 provides foradditional separation of the energy from the tissue. Finally, anylocalized heating is effectively removed by the passage of the coolingmedium along the outer conductor 32 through cooling catheter 43. Theresult of such an arrangement with the cooled ablation catheter 16housed within the extended working channel 18 is that greaterflexibility in the ablation catheter 16 can be achieved due to theabsence of a balun, without experiencing the localized heating drawbackswhich can affect ablation catheters without the emissions controllingfeatures of a balun.

Referring to FIGS. 3A and 3B, partial views of the extended workingchannel 18 are shown. In one embodiment, the extended working channel isformed of two layers, a non-conductive or insulative outer layer 34 anda conductive inner layer 28. Insulating layer 34 may be formed of amedical grade flexible plastic or polymer material. The conductive innerlayer 28 may be formed of a braided metallic material and substantiallysecured to the inner surface of the insulating layer and extends alongthe entire length of the inner wall of the extended working channel 18.Though depicted in FIG. 3B as concentric layers, the conductive innerlayer 28 could also be imbedded in the insulative outer layer 34. Theextended working channel 18 may be formed by overmolding plastic to forman outer non-conductive or insulative layer 34. The extended workingchannel 18 has a proximal end 21 and a distal tip 25, respectively. Theextended working channel 18 is formed to receive the ablation catheter16 (shown in FIG. 2), and, in at least one embodiment, to provide apathway for a cooling medium to either circulate within the extendedworking channel 18, or to pass through the extended working channel, inboth instances to cool the ablation catheter 16 when energized.

In one embodiment, a hub portion 26 is formed at the proximal end 21 ofthe extended working channel 18 and includes a locking mechanism 24configured to engage the ablation catheter 16. The locking mechanism 24may include a slot 27 that extends along the hub portion 26. The slot 27includes a plurality of mechanical interfaces 29 (shown in FIG. 4)positioned along the opposing wall portions that define the slot 27. Themechanical interfaces 29 may be in the form of detents, protrusions, orthe like that are configured to releasably engage a correspondingmechanical interface 33 (shown in FIGS. 2 and 4) provided at a proximalend of the ablation catheter 16. Engagement between the mechanicalinterface 33 and the plurality of mechanical interfaces 29 selectivelylocks the ablation catheter 16 into place within the extended workingchannel 18. As will be appreciated, other locking mechanisms may beemployed within the scope of the disclosure.

In the embodiment of FIG. 3A, indicia are provided along the slot 27adjacent the mechanical interfaces 29 (shown in FIG. 4) of the slot 27and represent quarter-wavelength increments of a desired frequency of asignal transmitted from the ablation catheter 16. In embodiments, eachmechanical interface 29, starting with the first mechanical interface29, represents a quarter-wavelength value; thus, the first mechanicalinterface 29 represents a quarter-wavelength, the second mechanicalinterface represents a half-wavelength, and so on. The selection ofquarter wave increments may enable the ablation catheter 16 and its useto be tuned to achieve a particularly desired ablation pattern.

Though described above with reference to an unchoked ablation catheter,the ablation catheter 16 may also incorporate a modified choke, asdescribed in various embodiments below, without departing from the scopeof the present disclosure. For example, in some embodiments, as shown inFIG. 2 a thin layer of insulating material 60 (e.g., a layer ofpolyethylene terephthalate (PET)) may be used to cover a portion of theouter conductor 32. This layer of insulating material 60 may assist inmaintaining the braided configuration of the outer conductor 32, or mayform part of a modified balun configuration.

In such a modified choke, the conductive inner layer 28 is only providedin a portion of the extended working channel 18. The electricallyconductive inner layer 28 is shorted to the outer conductor 32 of themicrowave ablation catheter 16 at a desired location immediatelyproximal a proximal end of the insulating material 60, thus creating achoke or balun by the combination of the conductive inner layer 28 andthe insulating layer 60. In one example, the conductive inner layer 28extends along an inner wall of the extended working channel 18 adistance that is approximately equal to a quarter-wavelength of adesired frequency of the signal being transmitted from the ablationcatheter 16.

Upon extension of ablation catheter 16 out of the distal end of theextended working channel 18, contact is made between balun shorts 62 andthe conductive inner layer 28 of the extended working channel 18,creating a balun from the combination of the extended working channel 18and the ablation catheter 16. As will be appreciated, coordination ofthe location of the conductive inner surface 28 and the location of thebalun shorts 62 is required to achieve the desired effect.

In a further embodiment a plurality of balun shorts 62 may be placedalong the inner conductor 32 in quarter wavelength increments, resultingin a tunable microwave ablation catheter, whose position may be changedduring the course of treatment to achieve a desired tissue effect. Aswill be appreciated, embodiments where the inner surface 28 of theextended working channel 18 is shorted to the outer conductor 32 of theablation catheter will require electrical contacts to be placed on thecatheter surrounding the ablation catheter and where necessary on thecooling catheters 43 in order to achieve the electrical short.

In an alternative embodiment of the present disclosure, an insulativelayer 30 which may be formed of polytetrafluoroethylene (PTFE) may beformed on an internal surface of the conductive inner layer 28 whichforms the inner wall of the extended working channel 18. In embodiments,the insulative layer 30 and/or the conductive inner layer 28 may bepositioned along the interior of the extended working channel 18 so thatthe insulative layer 30 and the conductive inner surface 28 incombination with one or more balun shorts 62 form the balun or choke.The internal diameter of the insulative layer 30 may be such that theouter conductor 32 of the coaxial cable 38 passes through the insulativelayer in sliding engagement when the ablation catheter 16 is in one ofthe aforementioned extended configurations. The insulative layer 30and/or the conductive inner surface 28 and their ultimate orientationwith respect to the outer conductor 32 can be adjusted duringmanufacture to control an overall phase, energy field profile, and/ortemperature response of the ablation catheter 16.

As noted above, the ablation catheter 16 may be used in conjunction withthe extended working channel 18 in several forms including cooled anduncooled. In one cooled embodiment, the ablation catheter 16 includesone or more columinal cooling catheters 43 which fully encapsulate thedistal radiating portion 42. In a second cooled configuration nocoluminal cooling catheters 43 are used and instead the coaxial cable 38with radiating portion 42 is simply inserted through the extendedworking channel 18 and cooling medium is allowed to pass through theextended working channel 18 to cool the radiating portion 42. Thisembodiment is an open cooling solution and the cooling medium is allowedto escape through the extended working channel 18 into the patient. In athird configuration which permits partial cooling of the coaxial cable38 up to an insulative layer 30 which is sized to allow slidingengagement of the coaxial cable 38, the radiator 35 of the ablationcatheter 16 is not cooled, and any cooling medium directed into theextended working channel 18, may not pass beyond the insulative layer30, but the remainder of the coaxial cable 38 is cooled. The balunshorts 62, if employed, may be spaced such that they do notsignificantly impede the flow of the cooling medium. Cooling medium,such as CO₂ gas or de-ionized water, may also form part of the balun,providing an additional insulative layer which operates in concert withthe conductive layer 28 and the balun short 62 to achieve the desiredeffect.

Still further, although the microwave ablation catheter 16 describedhere may be specific, it should be understood to those of skill in theart that other microwave ablation catheter embodiments, eithersimplified or more complex in structural detail, may be employed withoutdeparting from the scope of the instant disclosure.

Operation of the EMN system 10 to reach an identified target and enablethe treatment of target tissue within a lung of a patient is describedwith reference to FIGS. 1 and 4. As an initial step, imaging of apatient “P” is typically undertaken. For example, CT images may be takenand imported into a pathway planning software. One such pathway planningsoftware is the ILOGIC® Planning suite currently sold by Covidien LP.Typically, in such pathway planning software, the images are viewed anda clinician can identify targets within the images and generate pathwaysto arrive at the targets. The physician, or user, may use a prior CTscan of the patient “P” and software to construct a representation ofthe patient's luminal network to help determine and plan pathways to theidentified target location. Once the pathway is identified and accepted,this pathway becomes a navigation plan which may be exported tonavigation software such as the ILOGIC® Navigation suite currently soldby Covidien LP.

The patient “P” is then placed within the EMN system 10, as depicted inFIG. 1. The location of the patient “P”, and particularly featureswithin the luminal structure being navigated (e.g., the lungs) areregistered to the images of the navigation plan. Computer system 82, inoperation with a tracking module 80, determines the position of thepatient “P”, and thereby defines a set of reference coordinates, whichare matched with the images of the navigation plan. As a result, thenavigation software is able to superimpose the location of the sensor 22onto the images of the navigation plan, and depict to the user theresult of the manipulations of the catheter guide assembly 11, 12 on theimages of the navigation plan. This system also allows the user tofollow the pathway depicted in the navigation plan.

The EMN system 10 utilizes a six degrees-of-freedom electromagneticposition measuring system according to the teachings of U.S. Pat. No.6,188,355 and published PCT Application Nos. WO 00/10456 and WO01/67035, the entire contents of which are hereby incorporated byreference. A transmitter arrangement 76 is implemented as a board or matpositioned beneath patient “P.” A plurality of reference sensors 78 areinterconnected with a tracking module 80 which derives the location ofeach reference sensor 78 and sensor 22 in 6 degrees of freedom. One ormore of the reference sensors 78 (e.g., 3 reference sensors 78) areattached to the chest of patient “P” and their 6 degrees of freedomcoordinates are sent to a computer 82 where they are used to calculatethe patient coordinate frame of reference.

Once a bronchoscope 72 is inserted into the lungs of a patient “P”, theextended working channel 18 and guide catheter assembly 11, 12 includinglocatable guide 20 and sensor 22 are inserted into the bronchoscope 72.Bronchoscope 72 is connected to monitoring equipment 74, and typicallyincludes a source of illumination and a video imaging system. In certaincases, the locatable guide catheter assembly 12 and extended workingchannel 18 may be used without a bronchoscope. After advancing thebronchoscope 72 and catheter guide assembly 11, 12, including theextended working channel 18 and the locatable guide 20, to a point ofbeing wedged within a luminal network of the lung, the extended workingchannel 18 and locatable guide 20 are further advanced along theidentified pathway to the target “T”. Working in conjunction with theEMN system 10, the guide catheter assembly 11, 12 is used to guide theextended working channel 18 through the luminal network of the patient“P” to the target following the planned pathway relying on the sensedlocation of the sensor 22 as depicted on the images in the navigationsoftware.

Once at the identified target, the locatable guide 20 may be withdrawnand the extended working channel 18 becomes a pathway to the target “T”for subsequent diagnostic and treatment tools (e.g., biopsy tools, aguide wire, access tools, ablation catheter 16, etc.). Typically, theclinician may seek to take several biopsy samples to confirm that thetarget “T” is in need of treatment. In some cases, the target tissue maybe directly accessed from within the lumen (such as for the treatment ofthe endobronchial wall for COPD, Asthma, lung cancer, etc.). However, inother instances the target is outside the luminal walls of the bronchialtree and use of the extended working channel 18 and locatable guide 20alone do not achieve access to the target. Additional access tools maybe required to pierce or sever tissue, exit the lumen, and access thetarget tissue (such as for the treatment of disease within theparenchyma). In embodiments, the target tissue “T” may be pierced orpenetrated to allow placement of the radiator 35 of the ablationcatheter 16 within the target “T” (e.g., centered within the mass fortreatment). For example, a guide wire, piercing tool, a biopsy tool orthe distal radiating section 42 of the ablation catheter 16 may beutilized to pierce or penetrate the target “T.”

If it is determined that the target “T” requires treatment (e.g.,ablation), the ablation catheter 16 may be positioned through thebronchoscope 72 and the extended working channel 18 to enable treatment.Placement of the ablation catheter 16 may occur after the extendedworking channel 18 has been navigated to the target “T.” Alternatively,particularly in embodiments where sensor 22 is incorporated into theextended working channel 18 or into the ablation catheter 16 itself, themechanical interface 33 of the ablation catheter 16 may be engaged withone of the plurality of mechanical interfaces 29 of the lockingmechanism 24 and the extended working channel 18 and ablation catheter16 may be navigated to the target “T” together. In either case, beforeenergization of the ablation catheter 16, the radiator 35 must beextended to a position distal to the distal end 25 of the extendedworking channel 18 as the conductive inner surface 28, whichbeneficially acts as a Faraday cage, as described above, will alsosubstantially prevent radiation from escaping the extended workingchannel 18 and radiating tissue.

One or more imaging modalities may be utilized to confirm that theablation catheter 16 has been properly positioned (e.g. within thetarget “T”.) For example, computer tomography (CT), ultrasound,fluoroscopy, and other imaging modalities may be utilized individuallyor in combination with one another to confirm that the ablation catheter16 has been properly positioned within the target “T”. One methodologyemploying both CT and fluoroscopy imaging modalities is described incommonly assigned U.S. application Ser. No. 12/056,123 filed on Mar. 26,2008 by Dorian Averbruch and entitled “CT-Enhanced Fluoroscopy,” theentire contents of which are hereby incorporated by reference. Once itis confirmed that the ablation catheter 16 is properly positioned withinthe target tissue “T,” a user may begin with the ablation procedure andapply desired levels of microwave energy to the target “T” to achievethe desired ablation effect.

During the ablation procedure, as the temperature of the target “T”increases, the overall impedance at the tissue site may change, whichmay lead to an unbalanced signal between the inner and outer conductors40 and 32. According to one embodiment, to balance the signal, a usercan move ablation catheter 16 distally to disengage the mechanicalinterface 33 of the ablation catheter from the mechanical interface 29on the extended working channel 18, which moves the distal radiatingsection 42 further from the outer conductive layer 28. If need be, theuser can move mechanical interface 33 into engagement with one of theother mechanical interfaces 29 (e.g., the one that corresponds to ahalf-wavelength) of the extended working channel 18 to lock the distalradiating section 42 into this further position.

In yet another alternative embodiment of the present disclosure, theextended working channel 18 may comprise of or may be replaced by ametal hypo tube 36, as depicted in FIG. 5. In this embodiment, the metalhypo tube 36 contains a conductive inner surface 37 and may beoptionally coated on its exterior surface with an insulating material asdescribed above with respect to EWC 18. Similar to the conductive innerlayer 28 (See FIG. 3A), conductive inner surface 37 functions as anelectromagnetic shield for a microwave ablation catheter 16. Asdescribed above, the metal hyptotube 36 is configured to receiveinstruments including the locatable guide catheter 20 and sensor 22,biopsy tools and microwave ablation catheter 16, as well as otherswithout departing from the scope of the present disclosure. During anablation procedure, metal hypo tube 37, or extended working channel 18including metal hypo tube 36, is inserted into a patient and positionedadjacent to, or within, target tissue “T.” The ablation catheter 16 isthen placed within the metal hypo tube 36 and extended past the distalend of the metal hypo tube 36. In one embodiment, the metal hypo tube 36may be inserted along with an ablation catheter 16 having a pointed orpiercing configuration capable of piercing through tissue “T” (asdepicted in FIG. 5). Although FIG. 5 depicts ablation catheter 16 with apointed configuration, the end of the ablation catheter 16 may includeany suitable configuration including but not limited to a bluntconfiguration, flat configuration, hemispherical configuration, bar-bellconfiguration, tissue piercing configuration, etc. Once the tip of theablation catheter 16 is placed in the target tissue “T,” the metal hypotube 36 may be retracted to expose radiator 35 of the ablation catheter16. As explained in greater detail above, the extension of the radiator35 out of the extended metal hypo tube enables the ablation of tissue,but the length of that extension can be varied as desired to adjust theshape and size of the ablation zone.

While several embodiments of the disclosure have been shown in thedrawings, it is not intended that the disclosure be limited thereto, asit is intended that the disclosure be as broad in scope as the art willallow and that the specification be read likewise. Therefore, the abovedescription should not be construed as limiting, but merely asexemplifications of particular embodiments. Those skilled in the artwill envision other modifications within the scope and spirit of theclaims appended hereto.

What is claimed is:
 1. A microwave ablation catheter assemblycomprising: an ablation catheter including: a coaxial cable having aproximal portion and a distal portion, the proximal portion capable ofbeing operatively connected to a microwave energy source, the coaxialcable including an inner conductor and an outer conductor; and aradiator disposed at the distal portion of the coaxial cable; and anextended working channel configured to receive the ablation catheter forpositioning the radiator adjacent target tissue, the extended workingchannel including an electrically conductive inner surface, wherein,upon application of microwave energy to the microwave ablation catheterassembly, energy conducted along the outer conductor of the coaxialcable is captured within the conductive inner surface of the extendedworking channel and prevented from affecting tissue adjacent theextended working channel.
 2. The microwave ablation catheter assemblyaccording to claim 1, wherein the ablation catheter and extended workingchannel are placed within the patient using a location sensing system.3. The microwave ablation catheter assembly according to claim 1,wherein the extended working channel includes a slot at its proximal endconfigured to releasably engage with a corresponding mechanicalinterface positioned on the ablation catheter.
 4. The microwave ablationcatheter assembly according to claim 3, wherein the mechanical interfaceis moveable with the slot to lock the distal radiating section of thecoaxial cable into at least one of a plurality of positions definedwithin the slot.
 5. The microwave ablation catheter assembly accordingto claim 4, wherein indicia is provided along the slot.
 6. The microwaveablation catheter assembly according to claim 5, wherein the indiciarepresents quarter-wavelength increments.
 7. The microwave ablationcatheter assembly according to claim 1, wherein the extended workingchannel further comprises an insulator separating the electricallyconductive inner surface from tissue adjacent the extended workingchannel.
 8. The microwave ablation catheter assembly according to claim1, wherein the inner conductor of the coaxial cable extends distallypast the outer conductor of the coaxial cable and is in sealedengagement with the distal radiating section.
 9. The microwave ablationcatheter assembly according to claim 1, wherein the ablation catheterfurther includes one or more cooling catheters surrounding the coaxialcable and radiator to provide a pathway for a cooling medium.
 10. Themicrowave ablation catheter assembly according to claim 9, wherein thecooling medium is a liquid or gas.
 11. The microwave ablation catheterassembly according to claim 1, wherein the extended working channelprovides a closed pathway for a cooling medium to circulate within theextended working channel.
 12. The microwave ablation catheter assemblyaccording to claim 1, wherein the extended working channel provides anopen pathway for a cooling medium to pass through the extended workingchannel.
 13. A method of electrosurgically treating target tissue,comprising: positioning an extended working channel adjacent targettissue, the extended working channel having an electrically conductiveinner surface; inserting an ablation catheter through the extendedworking channel such that a radiator of the ablation catheter extendsbeyond the distal end of the extended working channel, the ablationcatheter having an outer conductor; applying energy to the ablationcatheter such that electrosurgical energy radiates from the radiator,wherein, upon application of energy to the ablation catheter any energyconducted along an outer conductor of the ablation catheter is capturedwithin the electrically conductive inner surface of the extended workingchannel and prevented from affecting tissue adjacent the extendedworking channel.
 14. The method according to claim 13, wherein insertingthe ablation catheter through the extended working channel furtherincludes engaging a mechanical interface of the ablation catheter withat least one mechanical interface defined along a slot provided on theextended working channel to lock the radiator of the ablation catheterin a position that is distal of the distal end of the extended workingchannel.
 15. The method according to claim 13, wherein the electricallyconductive inner surface of the extended working channel includes abraided configuration.
 16. The method according to claim 14, wherein aslot is provided at a proximal end of the extended working channel andis configured to releasably couple to a mechanical interface positionedon the ablation catheter.
 17. The method according to claim 14, whereinindicia is provided along the slot.
 18. The method according to claim17, wherein the indicia represent quarter-wavelength increments.
 19. Themethod according to claim 18, including moving the mechanical interfaceof the ablation catheter distally to lock the ablation catheter into atleast one other position within the slot to adjust a signal balancebetween inner and outer conductors of the ablation catheter.
 20. Amicrowave ablation system comprising: a microwave energy source; anablation catheter including: a coaxial cable having a proximal portionand a distal portion, the proximal portion being operatively connectedto the microwave energy source, the coaxial cable including an innerconductor and an outer conductor; and a radiator disposed at the distalportion of the coaxial cable; and an extended working channel configuredto receive the ablation catheter for positioning the radiator adjacenttarget tissue, the extended working channel including an electricallyconductive inner surface, wherein, upon application of microwave energyto the ablation catheter, energy conducted along the outer conductor ofthe coaxial cable is captured within the conductive inner surface of theextended working channel and prevented from affecting tissue adjacentthe extended working channel.